Education. Initially, he studied grammar, logic and arts in schools of Valencia; later, in 1492, he went to study at the University of Lérida and obtained a doctorate in utroque iure, both canon and civil law.

Early life. Lector at the University of Lérida. In 1408, Antipope Benedict XIII named him assessor and official of the diocese of Lérida. Canon of the cathedral chapter of Lérida in 1411. Around this time, Vicente Ferrer, future saint, prophesied his elevation to the papacy. Elected delegate of the diocese of Lérida to the Council of Constance in 1416; he did not participate in the assembly because right after the election, King Alfonso V el Magnánimo of Aragón ascended the throne and he was opposed to the celebration of the council; instead, Canon Borja went to Barcelona to represent his diocese in the synod of the church of Aragón. In 1418, he was charged with dealing with Cardinal Alamanno Adimari, archbishop of Pisa, who was the envoy of Pope Martin V to obtain the support of King Alfonso V; Canon Borja strongly cared for the reestablishment of the unity of the Church and his influence with the Aragonese monarch was decisive in the conclusion of the accord between the king and the new pope; in recompense, he received a canonship in the cathedral chapter of Barcelona. In 1418, he was named rector of San Nicolás of Valencia. He was in Italy from 1420 until 1423; he left from Los Alfaques on May 13, 1420; and returned to Barcelona in December 1423. From 1420 to 1423, he was also vice-chancellor of the University of Lérida; in that latter year, he resigned his offices at the university and diocese of Lérida to dedicate all his energies to the service of the king.

Sacred orders. (No information found).

Episcopate. In 1424, he was named administrator of the see of Mallorca; at that time, the king wanted him to be elevated to the cardinalate but Pope Martin V did not accept the request. Private secretary and counselor of King Alfonso V around 1425. He was one of the premier juris consults of his time. In 1429, Cardinal Pierre de Foix, O.F.M. went to Barcelona to obtain the resignation of Antipope Clement VIII, who had sought refuge since the end of 1424 in the fortress of Peñíscola; the cardinal asked the assistance of Canon Borja, who with only one companion went to Peñíscola and convinced the antipope to resign his pretensions; finally, the schism had ended. In reward, he was promoted to the episcopate. Elected bishop of Valencia, August 20, 1429; retained the see after his election to the papacy and occupied it until his death. Consecrated, August 31, 1429, by Cardinal Pierre de Foix, O.F.M.; in Peñíscola, he authorized Pedro Lloréns to take possession of the see in his name. In 1432, the king called him to Italy to resume his charge as royal counselor; the king had thought of sending him to the Council of Basel in 1432 but for diffreent reasons he never went and the council ended without his participation. At this time, he was in Tarazona, negociating with Castilla; and later in Navarra, but he never left Spain. In 1436, he returned to Spain to care for King Alfonso's illegitimate son, Ferrante, of whom he was the tutor for some time. In 1439, he guided the Aragonese delegation to the Council of Florence; there he met Cardinals Bessarion and Giuliano Cesarini and for the first time established contact with the papal court. When the king finally established himself in Naples in 1442, Bishop Borja was charged with the reorganization of the judicial system of the kingdom.; he also became president of the Royal Council; and of the Royal Council from 1442 to 1444; he strenuously resisted the project of King Alfonso of supporting the Council of Basel in order to force Pope Eugenius IV to recognize his claim to the kingdom of Naples. Sent by the king before Pope Eugenius IV in 1443 to negotiate with Cardinal Trevisano a final agreement between the king and the pope that culminated with the Treaty of Terracina, signed in June of that year and accepted by the pope on the following July 6. As recognition and reward for his mediation, he was promoted to the cardinalate.

Cardinalate. Created cardinal priest in the consistory of May 2, 1444; he entered Rome on July 12, 1444 and received title of Ss. Quattro Coronati. He took up residence in Rome in a palace near the Colosseum; and abandoned his royal services to devote himself exclusively to the service of the church. He was inscribed in the Brotherhood of the Holy Spirit in Rome on April 10, 1446. He was noted in the Roman Curia on February 21, 1447. Participated in the conclave of 1447, which elected Pope Nicholas V. Attended the secret consistory of October 27, 1451. Participated in the conclave of 1455 and was elected pope. He was very austere, charitable and conducted a very good life.

Papacy. Elected pope on April 8, 1455. Took the name Callistus III. He was crowned on April 20, 1455, in the steps of the patriarchal Vatican basilica, by Cardinal Prospero Colonna, protodeacon of S. Giorgio in Velabro. During his pontificate, he created nine cardinals in two consistories.

Death. August 6, 1458, Rome. Buried in a magnificent monument, built by his nephew Cardinal Rodrigo, in the chapel of S. Maria delle Febri, near the patriarchal Vatican basilica; the fragments of the monument are in the grotto of the basilica; during the reconstruction of the basilica, his remains were transferred in 1586 to another place of the church until 1605; later, they were transferred, together with the remains of Pope Alexander VI on January 30, 1610, to the church of S. Maria in Montserrato, the church of the crown of Aragón in Rome. On August 21, 1889, the remains were transferred to a modern tomb, work of Spanish sculptor Felipe Moratilla, with the medallions of both popes, in the chapel of S. Diego, in that church (now the Spanish national church in Rome and a cardinalitial title since 2003). In his will, he left 5,000 ducati to found a hospital in the house where he had lived as a cardinal.

(1) This is according to his genealogy, linked above; Mallett, "Callisto III." Enciclopedia dei papi, II, 658, says that her last name was Marti; his first biography in Spanish, linked above, indicates that his second last name (presumably his mother's last name) was Cabanillas.